Heating and cooling systems typically maintain temperature control in a structure by circulating a fluid within coiled tubes such that passing another fluid over the tubes effects a transfer of thermal energy between the two fluids. A primary component in such a system is a compressor which receives a cool, low pressure gas and by virtue of a compression device, exhausts a hot, high pressure gas. One type of compressor is a screw compressor, which generally includes two cylindrical rotors mounted on separate shafts inside a hollow, double-barreled casing. The side-walls of the compressor casing typically form two parallel, overlapping cylinders which house the rotors side-by-side, with their shafts parallel to the ground. Screw compressor rotors typically have helically extending lobes and grooves on their outer surfaces forming a large thread on the circumference of the rotor. During operation, the threads of the rotors mesh together, with the lobes on one rotor meshing with the corresponding grooves on the other rotor to form a series of gaps between the rotors. These gaps form a continuous compression chamber that communicates with the compressor inlet opening, or “port,” at one end of the casing and continuously reduces in volume as the rotors turn and compress the gas toward a discharge port at the opposite end of the casing for use in the system.
These rotors rotate at high rates of speed, and multiple sets of rotors (compressors) may be configured to work together to further increase the amount of gas that can be circulated in the system, thereby increasing the operating capacity of a system. While the rotors provide a continuous pumping action, each set of rotors (compressor) produces pressure pulses as the pressurized fluid is discharged at the discharge port. These discharge pressure pulsations act as significant sources of audible sound within the system.
To minimize the undesirable sound, noise attenuation devices or systems can be used. Examples of noise attenuation systems include a dissipative or absorptive muffler system and a restrictive muffler system that subjects the refrigerant to a tortuous path, each typically located at the compressor discharge. Mufflers typically cause a significant pressure drop downstream of the compressor discharge which reduces system efficiency.
What is needed is a muffler that sufficiently attenuates pressure pulsations generated by compressor operations without adversely affecting compressor operating efficiency.